The overall objective of the proposed research was to develop and test methods for the estimation of Mg availability from foods, using the stable isotope 26Mg. Previous work on this project has established conditions for oral dosage, timing and nature of samples appropriate for measuring 26Mg absorption in rats and man. Two methods of isotope detection, neutron activation and mass spectrometry have been established and compared. Mass spectrometry was found the more sensitive and precise method. Spinach, collard greens, turnip tops and leaf lettuce have been labeled with 26Mg. Future plans are to test these vegetables in rats and human subjects a) to ascertain whether extrinsic 26Mg is exchangeable with intrinsic 28Mg; b) to measure relative Mg availability from these foods, using MgCl2 as a standard. The same foods will be subjected in vitro various treatments that may release magnesium to investigate whether in vitro behavior of Mg in these foods can predict Mg availability in man.